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Articles by J. Alex Knoll

Our atmosphere tints summer moons

The moon waxes through the weekend, reaching full phase Tuesday, June 2. This time of year the moon follows a low, lazy arc above the southern horizon. At such a low angle to the horizon, before reaching our eyes the moon’s light must cut through much more of earth’s atmosphere than in winter, when the moon shines high overhead. Gases and trapped moisture within the atmosphere combine to tint the image we see a red, orange or yellow, which explains the names of June’s full moon: the Strawberry Moon, the Rose Moon and the Honey Moon.
    Friday night, the moon is joined by Spica, the blue-white first-magnitude star of Virgo, which is just a few degrees below and to the right of the moon.
    Saturday the moon has pulled westward and is midway between Spica to its right and Saturn to its left. Sunday the moon is less than 10 degrees to the left of Saturn, and Monday it is just two degrees to the the left of Saturn with red-orange Antares a few degrees below.
    Having just reached opposition, its closest point to earth and dead-opposite the sun, Saturn rises as the sun sets, is high overhead at midnight and sets with daybreak. Shining at zero magnitude, Saturn is brighter than it’s been in eight years. Better yet, its rings are positioned to allow the best possible viewing and appear all the brighter so close to opposition.
    Saturn isn’t the only planet visible after dark. Sunset reveals Venus high in the west and Jupiter 20 degrees higher still. Night to night, Venus is gaining ground on Jupiter leading to a grand conjunction in late June. Monday Venus forms a near-stright line with the Gemini twins Pollux and Castor.
    By late-evening the stars of the Summer Triangle are perched above the east horizon. Farthest west is the brightest and the fifth-brightest star, Vega, of the constellation Lyra. Off to the southeast of Vega and almost as bright is Altair of Aquila the eagle. Closing the triangle is first-magnitude Deneb, the head of Cygnus the swan.

After almost 4,000 days in space, this probe died for science

This week Mercury shows its best face in homage to the Messenger spacecraft, which crashed into the planet early morning April 30.
    The craft was launched in August 2004 and reached Mercury in March 2011, the first to orbit the innermost planet. Since then it has circled Mercury more than 4,100 times, compiling more data in the process than everything combined before that.
    Thursday, April 30, scientists at Johns Hopkins Applied Physics Lab cut life support on their prodigy, and shortly thereafter the craft fell from orbit, plummeting to the surface at more than 8,750 miles an hour. Messenger was already running on borrowed time, having exhausted its traditional fuel supply, but programmers were able to supplement it with helium onboard for other reasons. Now that, too, is exhausted.
    “I guess the end is coming,” the Messenger team posted earlier on Twitter “After 10 years, spacecraft will end life as just another crater on Mercury's surface.” A big crater, more than 50 feet wide.
    The elusive planet is not only difficult to spot, it had been difficult to study before Messenger. Less than 45 percent of Mercury’s surface had even been photographed, and that decades ago. In its four years in orbit, Messenger sent more than a quarter-million photos back to earth. it found volcanoes, discovered polar caps of frozen water and studied Mercury’s chemical makeup.
    Mercury “is crucial to developing a better understanding of how the planets in our solar system formed and evolved,” NASA explains on its Messenger website. “Mercury is an extreme: the smallest, the densest, it has the oldest surface, the largest daily variations in surface temperature — and it’s the least explored.”
    Mercury reaches its greatest elongation from the sun on May 7, climbing 20 degrees above the horizon. Look for it low in the west just after sunset this week. You may need binoculars close to sunset when it’s at its highest, but by 9pm it should easily be visible as it prepares to set. Much-brighter Venus is 20 degrees higher, and Aldebaran, the red eye of Taurus the bull is 10 degrees to Mercury’s left.
    These are the last nights to see Mars, which is even deeper in the glare of sunset than Mercury. Jupiter shines high in the south at nightfall, while Saturn rises around the same time. Look for the just-past-full moon near Saturn Monday and Tuesday night.

The moon visits the Beehive Cluster and more

The waxing moon reaches first-quarter phase Saturday, shining below and to the left of Jupiter. The moon is near the center of the constellation Cancer.
    Were the crab not on the ecliptic, it’s doubtful it would hold its place in the zodiac, as none of its stars are brighter than 3rd magnitude. (The ecliptic is the path of the sun, moon and planets as they circle through our skies.) But what it lacks in bright stars it makes up for in sheer quantity, as it hosts the Beehive Cluster. The Beehive is near the center of Cancer, about halfway between Regulus in Leo and Pollux in Gemini. Seen with the unaided eye, it appears as a dull smudge of light. However, binoculars or a small telescope reveal dozens of individual stars. But there’s even more to the Beehive than that, as it is a stellar incubator with thousands of infant stars.
    With binoculars at hand late Saturday and early Sunday, see if you can spot the ninth-magnitude asteroid Juno just above the moon. Your best chance is around 2am when the moon is about to set and the two appear above the west-northwest horizon.
    Sunday the moon is to the lower left of Jupiter, while above and to the left of the moon is the first-magnitude star Regulus, the three forming a near-perfect triangle. By Monday the moon lies just four degrees below Regulus.
    The five naked-eye planets are visible this week. Venus blazes in the west in evening twilight and sets in the west-northwest nearly two hours after dark. Scour the horizon below Venus for Mercury, appearing 30 minutes after sunset. The innermost planet is surprisingly bright, unlike Mars, which is just a few degrees to Mercury’s upper left. Jupiter shines high in the south as darkness falls and sets a little after 2am. Saturn rises with Scorpius around 10pm and is high in the south come dawn.

Equinox divides not only day and night but the seasons, too

The new moon winks from sight Friday, obscuring the sun in a total eclipse as seen in a narrow strip over northern oceans. Only residents of a few scattered islands between northern Great Britain and Greenland will see the full eclipse, but viewers across Europe and parts of Asia and Africa will see a partial eclipse.
    The nascent crescent moon returns just after sunset Saturday low against the western horizon. Look just above the crescent’s right tip for Mars, so faint you might need binoculars to see it. In contrast, Venus blazes a dozen degrees above the moon and puny Mars.
    The moon is much easier to spot Sunday evening, now to the left of Venus. About a fist-width to the upper right of the Evening Star, look for the second-magnitude star Hamal, the brightest in the minimalist constellation Aries.
    Monday, the waxing crescent moon shines well above Venus and below the Pleiades star cluster. Venus is so bright you can see it before the sun sets, but you’ll need full darkness to see the stars of the Pleiades, which make up the shoulder of the constellation Taurus. With the unaided eye, most people can see only six of the Pleiades, also known as the Seven Sisters. With binoculars, however, there are far more stars than sisters. The Pleiades is an interstellar incubator of gas and dust with thousands of stars dating back 100 million years. A mere 430 light-years from earth, the Pleiades is one of the nearest star clusters.
    Tuesday, the moon passes close to Aldebaran, the red eye of Taurus the bull, and the constellation’s other star cluster, the V-shaped Hyades. In Greek myth, these were nine sisters, daughters to Atlas and half-sisters to the Pleiades, which are off to the right. The Hyades mark the face of the bull.
    Friday’s vernal equinox ushers in spring for us in the Northern Hemisphere. At 6:45pm EDT, the sun hovers directly above the equator. High above the equator extending into space is another equally imaginary line, the celestial equator, which divides the heavens into a northern and a southern hemisphere. For the past six months, the sun has been in the southern celestial hemisphere, robbing us of more daylight the farther south it dips.
    Since winter solstice the sun has inched away from its southern nadir, and our days have grown longer. On the vernal equinox, the day is divided more or less equally between light and darkness.
    For the next three months, the sun climbs higher and higher into the northern celestial hemisphere before reaching its northern apex above the Tropic of Cancer on the day of summer solstice. Then it spends another three months slowly dipping southward to the second point of balance, the autumnal equinox.

Here on earth and in the skies, the seasons are changing fast

While our bodies are getting used to the hour shift brought about by Daylight Saving Time, Mother Nature is working fast to counter our dark mornings, and within a month day break will come at the same time it did before we switched our clocks.
    At no other point in the year do the days grow longer at a faster pace, as we gain more than three minutes of sunlight each day here in the Northern Hemisphere. Since solstice, December 21, we have gained more than an hour of sunlight in both the morning and at day’s end.
    These days of fast-growing light were called The Quickening by the ancient Celts. To them, all objects of earth — not just creatures, but trees, stones and the ground itself — were alive, all sharing the same sap of life. Now, deep within the still-bare trees, the sap of life flows, birds build new nests; shoots of the earliest spring flowers pierce the once-frozen soil. All around us, the earth’s pulse is picking up its pace.
    Overhead, too, the changing constellations foretell the coming of spring. The familiar shape of Leo the lion crouches over the eastern horizon, its blazing heart, Regulus, piercing the darkness.
    Following the great lion is Virgo, the goddess of crops and harvest, holding in her hand an ear of wheat in the form of the brilliant star Spica. Six months of the year the constellation is absent and the land falls into stasis as the goddess mourns her daughter Persephone’s confinement in the underworld with husband Hades. Now, with Persephone’s return, the mother’s grief ends and the land again begins to bloom.
    Next to rise is Boötes, the herdsman of the two bears, Ursa Major and Ursa Minor. In Greek legend, Boötes is Arcas, son of the nymph Callisto and Zeus and the first to harness a team of oxen to the plow, revolutionizing farming and ushering in the era of agriculture. Each year, Boötes returns to our evening skies to usher in the spring planting season.
    The scorpion Scorpius crawls over the eastern horizon as winter’s great hunter Orion sets in the west. In Greek myth, Orion had both jilted the goddess Artemis and boasted that he was the superior hunter. Enraged, she sent the scorpion to kill him. Look for the two stinger stars, Shaula and Lesath, less than one-half degree apart. Called the Swimming Ducks, this pair returns to morning skies to signal the coming of spring. From the Arabic Al Shaulah, the sting, Shaula is the 24th-brightest star in the sky, although it often goes unnoticed, as neither duck climbs high above the horizon at our latitude.
    Before dawn of Friday the 13th, the last-quarter moon shines near the head of Scorpius with ringed Saturn close by. The heart of the scorpion, the red-giant Antares, shines less than 10 degrees to the lower left of Saturn.
    Venus rules the early evening, perched above the western horizon and blazing at magnitude –4. A few weeks ago Mars appeared within a few degrees of Venus, but now the red planet well below and pulling farther away night by night.
    With sunset, Jupiter appears high in the east, perhaps the first “star” you see in the gathering night. as the stars come out. By 11pm it is nearly overhead, finally setting an hour before sunrise.

There’s work overhead on the ISS

Thursday evening the waxing gibbous moon stands above the constellation Orion, appearing as if it were the hunter’s head in profile. The next night it is above and to the left of Betelgeuese, Orion’s shoulder, and the two form a nice line with Rigel, the hunter’s foot. Saturday Luna is below the twins of Gemini, Castor and Pollux, and above Procyon, the lead star in the constellation Canis Minor, the Little Dog. Off to the east is brilliant Jupiter. Sunday the moon rests in the middle of a triangle formed by Pollux, Procyon and Jupiter. Come Monday, Luna is just five degrees south of Jupiter. Tuesday the moon is to the upper right of Regulus, with Jupiter well above them both. Then on Wednesday, the moon, Jupiter and Regulus form a loose triangle.
    While the moon is our only natural satellite, countless manmade satellites orbit the earth. You’ve likely seen some and presumed they were airliners passing overhead in the night. The International Space Station, however, stands out from the pack, shining brighter than except the sun and moon and zipping across the sky like a shooting star.
    This past week, on February 21 and 25, astronauts aboard the ISS completed two of three scheduled space walks to prepare it for future commercial dockings. The third is planned for Sunday, March 1.
    The ISS was originally designed to receive docking space shuttles, which were secured alongside a berthing port using the station’s robotic arm. Unmanned cargo vessels and Russian Soyuz rockets (the only means of sending and retrieving astronauts to and from the station now that the shuttles have been retired) continue to use this system.
    However, manned commercial vessels, set to begin arrival to the ISS in 2017, will maneuver into a docking port within the station itself — something akin to what we’ve seen in movies and television for decades.
    The current system is a daunting and time-consuming process, both arriving and departing. The new system will allow a quick evacuation of crewmembers from the station in the event of an emergency.
    While we won’t be able to see the ISS during the space walk, it routinely flies overhead. For dates and times, go to http://spotthestation.nasa.gov.

Mars and Venus together at dusk

An ever-so-thin sliver of moon appears low in the west at evening twilight Thursday briefly before sinking beneath the horizon. The Evening Star Venus blazes above and to the moon’s left, with much fainter Mars just above Venus.
    Sunset Friday finds the two-day-old crescent moon within two degrees of Venus and Mars, all so close they easily fit within the eyepiece of binoculars and modest backyard telescopes.
    Come Saturday evening, the moon is roughly 10 degrees above Venus and Mars. But now the two planets are less than one-half degree of one another, with Mars just to Venus’s upper right. Venus shines more than 100 times as bright as Mars, so much so that its light could obscure the red planet, in which case you’ll need those binoculars to discern it. After that, Venus climbs higher into the west and away from Mars.
    While Venus and Mars appear together this week, the planets are actually millions of miles apart. Closer to the sun, Venus completes one orbit in roughly 225 days, while Mars makes the loop in 687 days. From our fixed vantage point here on earth — which isn’t really fixed, as we, too, are always in motion around the sun — these planets cross paths several times each year. But with roughly 75 million miles separating the orbital line of one planet from the other, there’s a lot of variance, so a close conjunction like this is pretty rare. Venus and Mars haven’t appeared so close in our sky since 2008, and they won’t again for another two years.
    Jupiter is a fixture of the night sky. It appears in the east as twilight fades, and by 11pm it is almost directly overhead. By 5am it is low in the west-northwest and sets just before sunrise.
    If you’re up before dawn, look for golden Saturn to the south. It is traveling with the constellation Scorpius, whose return to the skies each year heralds the coming of spring. The red heart of the scorpion, Antares, shines almost as bright as Saturn and less than 10 degrees below and to the left.
    The last of the naked-eye planets is just eeking away from the glare of the sun. Look for Mercury just above the east-southeast horizon in early dawn. Binoculars will help you pinpoint it against the glare of the coming sun.
    Wednesday’s first-quarter moon shines amid the constellation Taurus the bull and is less than one-half degree from its glaring red eye Aldebaran. Above the moon a little farther are the stars of the Hyades cluster, and higher still those of the Pleiades cluster.
    Some of the brightest stars appear during these cold, dark nights. Orion the hunter stands above the southern horizon in the evening, the three stars of his belt pointing up to Taurus and down toward Canis Major and the brightest star, Sirius. Orion’s foot is marked by Rigel, while his shoulder is the red giant Betelgeuse, with Canis Minor and its bright star Procyon to the left. Above these stand the Gemini Twins, Castor the higher and brighter star and Pollux a little below it. Above and to the right of Gemini is Capella, the bright star of Auriga the charioteer, shining directly overhead at 8pm. To the east is Leo the lion and its bright star Regulus.
    Just east of Orion is the winter Milky Way, stretching from the southeast to almost directly overhead and then down to the northwest in the early evening.

Join the fight for dark skies

The waning crescent moon rises ever later in predawn skies this week. Friday it appears before 3am, and by 5am it is well placed above the southeast horizon, forming a tight triangle with golden Saturn to the right and red Antares, the heart of Scorpius, below. The ringed planet stands above the scorpion’s head, one degree of its uppermost, second-magnitude star Graffias.
    By Monday the moon is a thin crescent low in the southeast at 6am. If skies are clear and you have an open view of the horizon, you might be able to catch the reappearance of Mercury. Your odds will be better with binoculars. Look to the lower left of the moon’s outside arc. The next morning, the last remnant of the waning crescent rises within an hour of the sun, and now Mercury is just a few degrees to the right of its inner curve.
    Mercury never pulls far from the sun and does not climb high into the sky. Plenty of people may not even realize they have seen it when looking at an exceptionally bright “star” hugging the horizon at dawn or during evening twilight.
    You shouldn’t be as hard-pressed to spot our neighbors, Venus and Mars in the west-southwest at dusk. The two are only five degrees apart at week’s end, well within the field of view of binoculars or a telescope. By Wednesday they’ve cut the distance by half on the way to a one-half-degree conjunction on the 21st. There’s no confusing the two, as Venus blazes at –3.9 magnitude, while Mars smolders at first magnitude. In the exponential calculus of stellar magnitude, that means that Mars, as bright as your average star, is 99 percent dimmer than the Evening Star.
    Jupiter is a fixture of the night sky right now, rising in the east-northeast as twilight fades, almost directly overhead at midnight and clinging to the west-northwest horizon as daybreak approaches. To its right is the dim constellation of Cancer the crab, while to its left is the easy-to-identify Leo the lion.
    This week marks the latest installment of the Globe at Night campaign. Its goal is for ordinary people to record and submit their star counts. The target this time around is the constellation Orion, which is high in the south by 8pm. You can download star charts and instructions at www.globeatnight.org. Your results along with thousands from around the world help astronomers measure darkness and raise awareness about the threat of light pollution.

Lovejoy awaits at the edge of sight

Lovejoy awaits at the edge of sight

The waning gibbous moon rises around 8pm Thursday, with Jupiter high above it. Between them is the blue-white star Regulus of Leo the lion. Sunday the moon rises around 11pm, with the white star Spica 10 degrees beneath it. As daybreak approaches Monday morning, the two are even closer together high in the southwest. That evening the moon rises just before midnight, and now it is the one trailing Spica. Before dawn Thursday the 12th, the now-crescent moon shines within 10 degrees of golden Saturn, with Antares, the red heart of Scorpius, a little farther toward the horizon.
    The waning moon leaves the evening sky bereft of its powerful glow, making these next two weeks your best chance to spot  Comet Lovejoy before it’s gone forever — or at least the next eight thousand years. The fifth magnitude comet hovers at the border of naked-eye visibility between the constellations Perseus and Andromeda.
    Binoculars will bring it into view as a faint, oblong smudge, while even a modest telescope will reveal its brighter coma and trailing tail. You might even be able to discern the green-glowing head of the comet and its blue-hued tail. These colors are a tell-tale sign of the comet’s molecular composition, the green from diatomic carbon and the blue from carbon monoxide, both being charged by interstellar ultraviolet radiation. In contrast, naked-eye comets appear white, a result of sunlight reflecting off particles of dust and debris.
    Technically titled C/2014 Q2, the comet is named after amateur astronomer Terry Lovejoy, of Australia, who discovered it last August. Lovejoy has identified four earlier comets.
    Night by night, Comet Lovejoy is inching north, from the feet of Andromeda toward the outstretched arm of Perseus. By this time next month it will be one, if not two, magnitudes dimmer and much harder to find as it heads to the outer solar system.
    Closer to home, Venus and Mars hover above the west-southwest horizon at twilight on their way to a fabulous conjunction later this month. They are maybe a half-dozen degrees apart this weekend, the size of your fist held at arm’s length. And Jupiter shines from sunset to sunrise.

Can you spot the naked-eye five?

As the sun sets, look to the southwest for Venus. With a clear view of the horizon, you might spy Mercury below and to the right of Venus at week’s end, but the innermost planet’s viewing days are numbered. Roughly 15 degrees above Venus, look for the ruddy glow of Mars.
    Thursday and Friday evening the thin crescent moon joins the throng, somewhat between Venus and Mars the first night and above Mars, forming a horizontal line with Venus the next. Venus sets within an hour of the sun, while Mars sets around 8pm. But night by night, Venus is gaining about a minute of visibility, closing the gap with Mars in the process and leading to a conjunction of the two later next month.
    As these twilight planets set in the west, another rises in the east. Jupiter is hard to miss, as it is the brightest object in that part of the sky. By 9pm it is high in the east, at midnight is near the celestial zenith, and as dawn nears it is ablaze above the west horizon. A dozen degrees below the giant planet is fainter Regulus, which marks the dot of what looks like a backwards question mark. This asterism is called the Sickle of Leo and makes up the head of the larger constellation Leo the lion. A triangle of stars to the left of the sickle marks the lion’s haunches, the brightest being Denebola, which in Arabic means the lion’s tail.
    Saturn rises in the wee hours of the morning, and by 6am it is well-placed in the southeast. Its rings are tilted our way so that they stand out against the planet’s surface when viewed with even a small telescope. Saturn sits at the head of the constellation Scorpius, with its red heart Antares 10 degrees below the planet and the creature’s body trailing away toward the horizon.
    The moon waxes to first-quarter phase Monday, when it is almost directly overhead at sunset. Wednesday after sunset it is just a few degrees above and to the left of Aldebaran, the glaring eye of Taurus the bull, and the Hyades star cluster. Higher still are the stars of the Pleiades cluster, the Seven Sisters. While the moon’s light may make both clusters appear as fuzzy spots, simple binoculars will reveal many distinct stars in each.